Such an apparatus is known from the prior art and is illustrated schematically in FIG. 1, the input circuit having the reference numeral 10, the voltage converter apparatus the reference numeral 12 and the output circuit the reference numeral 14. The lamp is given the reference numeral 16. A more detailed illustration of the circuit arrangement used as the voltage converter apparatus 12 in the prior art can be seen in FIG. 2. This has, on the input side, an input capacitor C1 and, on the output side, an output capacitor C2. This circuit, which is shown here by way of example, is in the form of a step-down converter and has a switching apparatus T1, in this case a transistor, a freewheeling diode D1, a trapezoidal capacitor C3 and an inductance L1. Whilst the switching apparatus T1 and the inductance L1 are arranged in the series branch, the freewheeling diode D1 and the trapezoidal capacitor C3 are each arranged in a parallel branch. A trapezoidal capacitor serves the purpose of setting the switching speed of the switching apparatus. The inductance L1 is conventionally dimensioned as an energy-storage inductor and serves the purpose of maintaining a current flow following commutation.
On switching of the switching apparatus T1, very high current and voltage variation speeds result which can produce radio interference in the range from 20 to 200 MHz in the case of preferred applications of these circuits. In order to adhere to the statutory regulations, a damping element L2, preferably a ferrite, is therefore arranged in series with the switching apparatus T1. Depending on the frequency range, the damping element may also be in the form of an iron sheet or in the form of at least one conductor loop.
In the case of the use of a damping ferrite, in the prior art the latter is preferably threaded onto a transistor leg or is fitted as a separate component. Using such a damping element, the radiofrequency oscillations, which are produced by the switching of the switching element T1, are damped. The disadvantage of this known connection of the damping element consists in the fact that it requires a damping element which needs to be designed such that it represents a resistance which is as low as possible in the case of a direct current and which is as high as possible in the case of a radiofrequency alternating current. The ratio of the resistance given a direct current to the resistance given an alternating current is generally of the order of magnitude of 1:1000. The DC resistance is preferably below 100 mΩ, and the radiofrequency AC resistance should be of the order of magnitude of 100 Ω. In order to achieve these values, the damping element must be relatively large. This has the result that the damping element in the prior art cannot be realized in SMD, but must be mounted as a discrete component by hand on the printed circuit board. The size also has a negative effect on the space which is already limited in an electric ballast.
The present invention is therefore based on the object of developing a generic electronic ballast such that automatic assembly is made possible and a considerable reduction can be achieved in the space taken up by the damping element.